"We're trying to develop a range of instruments and sensors that are able to pick up concealed explosives, with a view to make sure people aren't injured when they're trying to detect these things out in the field," says Queensland University of Technology laser physicist Associate Professor Esa Jaatinen.

While trained sniffer dogs are able to pick up a range of different chemicals that are only present at 1 part per billion, the hunt is on for an artificial sensor that can do the same.

While very sensitive detectors have been developed before, they don't usually work for more than one or two materials, says Jaatinen. Alternatively tests of the sensors have given unreliable results.

Jaatinen and colleagues developed a sensor that is able to reliably detect four different nitroaromatic chemicals, like TNT and its derivatives, which are present in many explosives.

The key to the sensor is a one-millimetre square corrugated gold surface that picks up traces of explosives floating in the air in vapour form.

When laser light is shone onto the surface, the surface scatters and shifts the frequency of the light in a particular way, depending on the nature of the explosive chemical on it.

A detector picks up the scattered light and enables the sensor to work out which traces of nitroaromatics are present, if any.

Jaatinen says repeated tests showed the prototype, which is cheap to make and practical to use, gives reliable results.

He says a similar approach can be used to detect narcotics.

The research was carried out with a team from Melbourne's Swinburne University, led by Professor Saulius Juodkazis.

Improving sensitivity

The researchers now want to improve the sensitivity of the device, which is currently limited to picking up chemicals in concentrations of parts per million.

They also want to work out how to make the sensor reusable.

"We want to be able to do a detection and then in some way remove the material that's stuck to the sensor and reuse it without the operator having to wipe it off," says Jaatinen.

Ultimately, he says, the sensor would incorporate a vacuum that sucks air past a sensor located at the end of a 'wand'.

This would enable checking of an object from up to two metres away, says Jaatinen.

He says the technology would work in combination with a previously-developed patented system designed to roughly check for explosives from 50 to 100 metres away.

"Once you have established, from a distance, that it seems safe to proceed, then you go closer and do a more sensitive measurement with this sensor technology," says Jaatinen.